The present invention relates to loop suppression control relative to switch apparatuses on a backbone network and a network constituted by other switch apparatuses arranged under the switch apparatuses on the backbone network, in this network environment.
The IEEE 802.1D standard discloses STP (Spanning Tree Protocol) and GSRP (Gigabit Switch Redundancy Protocol) as a loop suppression function on a network. Generally, the above loop suppression function is activated in switch apparatuses arranged on a backbone network. On the contrary, in the case of the switch apparatuses arranged below the backbone network, there is frequent occurrence such that a port is frequently installed for an additional purpose, and the switch apparatus is often installed for a temporary purpose. Therefore, in the case where STP is activated in the above installed switch apparatus, the loop suppression function, such as STP etc., is sometimes not activated in the switch apparatuses since the backbone network is subject to an adverse effect frequently caused by topology changes. In this environment, when a loop failure occurs at the switch apparatus arranged below the backbone network, a loop detection function is sometimes activated in the respective switch apparatuses arranged below the backbone network since the entire network is subject to the adverse effect. For example, in the case of JP-A-2006-217496, a technique as a current loop detection function has been designed such that a loop detection frame is sent from respective ports of a switch apparatus, and the switch apparatus itself receives the same loop detection frame to deactivate the port receiving the loop detection frame, or deactivate the port by performing a port priority control.
Of the above related art, the STP disclosed in IEEE 802.1D is activated in the switch apparatuses arranged on the backbone network, however, it is not activated in a network (hereinafter, referred to as low-order network) constituted by switch apparatuses arranged below the switch apparatuses of the backbone network. Because of the above situation, in the case where a failure occurs on the network, a constitution of the switch apparatuses is changed by causing a recovery, and a switch apparatus is additionally installed on the network, this takes about several tens of seconds until a communication is made stable in the case of STP. During that time period, there arises a problem that the communication between the switch apparatuses is halted on the backbone network.
Further, the current loop detection function disclosed in JP-A-2006-217496 is a technique such that the loop detection frame is sent from the respective ports of the switch apparatus itself, and the switch apparatus itself receives the same loop detection frame to deactivate the port that received the loop detection frame and to deactivate the port by performing the port priority control. However, in the case of the switch apparatuses arranged on the backbone network, there are no means of sending the loop detection frame to the backbone network since STP is activated to carry out loop suppression. This is because there is a suppression spreading effect for a low-order network when a loop occurs, in the case of the switch apparatus in which STP is activated. However, when a loop occurs in the low-order network, not only the port (hereinafter, referred to as low-order port) on a low-order network receives the loop detection frame, but also the port (hereinafter, referred to as high-order port) on the backbone network sometimes receives that the loop detection frame as well. In this case, the entire low-order network is decoupled from the backbone network since the high-order port that has received the loop detection frame is deactivated.
In the JP-A-2006-217496, even though it is attempted to set the high-order port to a high priority to carry out the port priority control, there arises a problem that the low-order network is decoupled from the backbone network since the high-order port is deactivated when the loop detection frame sent from the high-order port is received by the same high-order port.